In the kraft method, the wood raw material is boiled with white liquor so that the lignin in the wood is dissolved and the cellulose fiber is exposed. The white liquor becomes black during boiling and is then referred to as black liquor. The cellulose fiber is filtered from the black liquor and then takes its own path in the plant, which is usually referred to as the fiber line. The black liquor is pumped away for recycling of chemicals and the production of new white liquor.
The wood raw material comprises approximately 1-4% extractive matter, primarily fatty acids, resin acids and neutral compounds, of which resin acids is only present in conifers. The fatty acids and the resin acids are saponified during boiling with the liquor and forms what is, within the mill, usually referred to as soap. Since the neutral compounds are hydrophobic they also end up in the soap phase. The soap must be separated from the black liquor, otherwise there will be problems during evaporation and possibly also in the recovery boiler, so it is of great importance to know the soap content of the black liquor during the different steps on the way to the recovery boiler. Current analytical methods depends on chemistry and takes long time to carry out, typically 2-4 hours, which results in that the estimated soap content at any time point refers to the actual soap content two to four hours earlier, unless the process is stopped during such a time period, which off course is unsuitable.
A purpose of the current invention is to provide a method for analysis for the measurement of soap content in black liquor which provides results faster than the currently known methods.
Another purpose of the invention is to provide an analytical container which is suitable to use with such an analytical method for the measurement of soap content in black liquor.
These and other goals are achieved by an analytical method and an analytical container.